The 72 weeks is just the longest follow up that has been done so far, and shows that the weight loss is maintained for that time if the person stays on the drug at the dose they used to lose the weight.
72 weeks really isn't the longest followup for patients on tirzepatide. The research followed individuals for 193 weeks in SURMOUNT. And if we look at the weight loss curves there is still a decline up to week 72, albeit a very modest one from week 60. It's difficult to tell, but it looks like on the 15mg curve that there is still some weight loss to week 85. Then all three curves flatline.
I've been thinking lately that given how close the 10mg and 15mg lines are in this chart that there is diminishing returns on higher doses. I'm not sure if a higher dose is really the solution to a stall as people approach week 72.

I'm literally on week 70 (and not at goal) so I have a slightly vested interest in what happens next. My gut is that alternative pathways, more protein, and resistance training are likely to break the stall than more tirzepatide.